Clonezilla is a partition or disk cloning tool
similar to Symantec Ghost. It saves and restores
only blocks in use on the hard drive if the file
system is supported. For unsupported file systems,
dd is used instead. It has been used to clone a 5
GB system to 40 clients in about 10 minutes.

Since v2.04, bash has allowed you to intelligently program and extend its
standard completion behavior to achieve complex command lines with just a few
keystrokes. Imagine typing ssh [Tab] and being able to complete on hosts from
your ~/.ssh/known_hosts files. Or typing man 3 str [Tab] and getting a list of
all string handling functions in the UNIX manual. mount system: [Tab] would
complete on all exported file-systems from the host called system, while make
[Tab] would complete on all targets in Makefile. This project was conceived to
produce programmable completion routines for the most common Linux/UNIX
commands, reducing the amount of typing sysadmins and programmers need to do on
a daily basis.

John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. It supports several crypt(3) password hash types commonly found on Unix systems, as well as Windows LM hashes. On top of this, lots of other hashes and ciphers are added in the community-enhanced version (-jumbo), and some are added in John the Ripper Pro.

Lynis is an auditing and hardening tool for Unix derivatives like Linux/BSD/Solaris. It scans systems to detect software and security issues. Besides security-related information, it will also scan for general system information, installed packages, and possible configuration mistakes. The software is aimed at assisting automated auditing, software patch management, and vulnerability and malware scanning of Unix-based systems.

Diskless Remote Boot in Linux (DRBL) provides a diskless or systemless environment for client machines. It works on Debian, Mandriva, Red Hat, Fedora, and SuSE. Unlike LTSP, it uses distributed hardware resources and makes it possible for clients to fully access local hardware. It also includes Clonezilla, a partitioning and disk cloning utility similar to Symantec Ghost.

Rootkit Hunter scans files and systems for known
and unknown rootkits, backdoors, sniffers, and malware. The
application consists of the main shell script, a few
text-based databases, and optional Perl scripts. It can recognise and run external applications like 'skdet' and 'unhide'. It should run on almost every Unix clone.

LEAF is a secure, feature-rich, customizable embedded Linux network appliance for use in a variety of network topologies. Although it can be used in other ways, it's primarily used as a Internet gateway, router, firewall, and wireless access point.

Apache Toolbox provides a means to easily compile
Apache (IPv4/6) SSL, PHP(v3/v4), MySQL, Jakarta, a
large number of modules (61 3rd party modules and
36 default Apache modules, static or as DSOs), and
GD libraries with PNG+JPEG+Freetype2+zlib support.
It is fully customizable and menu-driven.
Everything is compiled from source, and wget is
used to download any missing modules. It can also
check for RPMs that might cause problems and
create an RPM with your selections.

MailScanner is an email virus scanner, vulnerability protector, and spam tagger. It supports the Postfix, Sendmail, Exim, Qmail, and ZMailer MTAs, and the Sophos, McAfee, F-Prot, F-Secure, CommandAV, InoculateIT, Inoculan, eTrust, Kaspersky, Nod32, AntiVir, BitDefender, RAV, Panda, DrWeb, ClamAV, and other anti-virus scanners. It uses SpamAssassin for highly successful spam identification, and is designed to handle denial of service attacks. It will detect password-protected zip files and apply filename checking to their contents. It is very easy to install, requires no changes at all to your
sendmail.cf file, is designed to be lightweight, and won't grind your mail system to a halt with its load. It can be integrated into any email system, regardless of the software in use.